Lower molecular weight alcohols and ethers such as isopropanol (IPA) and diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have high blending octane numbers. In addition, by-product propylene from which IPA and DIPE can be made is usually available in a fuels refinery. An important aspect of research in the petroleum industry relates to processes to produce high octane lower aliphatic alkyl ethers as octane boosters and supplementary fuels.
The catalytic hydration of olefins, particularly C.sub.3 and C.sub.4 olefins, to provide alcohols and ethers is a well-established art. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,262,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,848; 3,989,762, among others.
Olefin hydration employing medium pore and large pore zeolite catalyst is a known synthesis method. As disclosed in U.S. Pat. No. 4,214,107 (Chang et al.), lower olefins, in particular propylene, are catalytically hydrated over a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of from 1 to 12, e.g., acidic ZSM-5 type zeolite, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product. Acid resin catalysts such as "Amberlyst 15" may also be used for hydration of light olefins.
The production of ether from secondary alcohols such as isopropanol and light olefins is known. As disclosed in U.S. Pat. No. 4,182,914, DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cationic exchange resin as catalyst. Recently, processes for the hydration of olefins to provide alcohols and ethers using zeolite catalyst such as ZSM-5 or zeolite Beta have been disclosed in U.S. Pat. Nos. 4.214,107 and 4,499,313 to Bell et al.; and U.S. Pat. Nos. 4,757,664, 4,857,664 and 4,906,187 to T. Huang. These patents are incorporated herein in their entirety by reference. One of the advantages in using zeolite catalyst for hydration and/or etherification of light olefins is the regenerability of the catalyst. Where resin based catalysts can decompose at the high temperatures required to remove deactivating amounts of carbonaceous deposits, zeolite catalysts remain thermally stable and can be regenerated oxidatively or in contact with hydrogen.
The hydration and etherification of lower olefins such as propylene to produce IPA and DIPE over a fixed bed of shape selective zeolite catalyst is generally carried out in liquid phase employing a feedstream comprising water and propylene at temperatures in excess of 200.degree. F. and high pressure, preferably above 1000 psi (7000 kPa). While attempting to maximize the rate of conversion, process conditions are selected to also reduce the more disadvantageous reactions which can occur during the process that could compromise the process advantages. These adverse reactions include the oligomerization of propylene, the formation of deactivating amounts of coke and carbonaceous deposits on the catalyst and the hydrothermal attack of water on the catalyst. These adverse reactions tend to find favor with increasing temperature and concentration providing a challenging limit to workers in the field with respect to reactor temperature.
Conventional methods to convert propylene to DIPE involves isopropyl alcohol synthesis, and subsequent reaction of alcohol with additional propylene to give diisopropyl ether. Formation of the initial carbon-oxygen bond in an alcohol by olefin hydration, such as the formation of isopropanol by hydration of propene is a difficult step that puts severe demands on acid catalyst stability. These stability problems are due to hydrolysis of the active catalyst sites by liquid-phase water, and appear common to acidic resin, sulfuric acid, and zeolite catalysts. In the conversion of an IPA feedstream and a C.sub.3 hydrocarbon feedstream comprising propene and propane to DIPE as conventionally practiced, the propylene conversion per pass is only about 20% or less. The reaction effluent is a mixture containing unreacted alcohol, propylene and propane, oligomeric hydrocarbon by-products, in addition to the DIPE product.
It is an objective of the present invention to provide a process for the conversion of propylene to diisopropyl ether or isopropanol with high selectivity.
A further objective of the invention is to provide a process for the conversion of propylene to diisopropyl ether or isopropanol with high selectivity by obviating the need to directly convert propylene to isopropanol by hydration of propylene with water.
Another object of he invention is to carry out the process using particularly selective shape selective zeolite catalysts, especially zeolite Beta.